Deposition of metal-rich mine tailings, metal smelting, leather tanning, electroplating, emissions from gas exhausts, energy and fuel production, downwash from powerlines, intensive agriculture and sludge dumping are the most important human activities which contaminate aqueous systems with water containing large amounts of toxic metals. The list of sites contaminated with toxic metals grows larger every year, presenting a serious health problem and a formidable danger to the environment. Water treatment procedures have been developed to remove metals from aqueous environments but they do a relatively poor job of removing toxic metals from residential and industrial aqueous waste, contributing to the overall problem.
Methods have been developed that utilize biologically active materials (e.g., higher plants) to remove toxic metals from wastewaters. Unfortunately, waste waters such as mine tailing drainage and water from smelting operations are nutrient poor and often contain concentrations of inorganic carbonaceous and nitrogenous nutrients that are insufficient to support growth of plants. Supplementation of metal-containing waste water with growth-promoting amounts of inorganic plant nutrients is problematic since the addition of external nutrients runs the risk of further pollution.